A brake device in an automatic transmission includes a rotatable rotation-side friction plate interconnected with a predetermined rotation element, and a non-rotatable fixed-side friction plate disposed to face the rotation-side friction plate. As the rotation-side friction plate and the fixed-side friction plate are brought into pressing contact with each other, rotation of the rotation-side friction plate is stopped (engaged state). As a result of release of the engaged state, rotation of the rotation-side friction plate is allowed (released state). In the brake device having the aforementioned configuration, for instance, when the brake device is switched from a released state to an engaged state, frictional heat due to sliding between the friction plates is generated. In particular, the brake device may be intentionally slip-controlled depending on the type of an automatic transmission. In other words, the brake device may be brought to an incompletely engaged state, When the aforementioned slip-control is performed, the amount of frictional heat generated by the slip-control may increase. This may cause deterioration of the brake device due to the frictional heat.
In view of the above, Japanese Patent No. 5,498,785 proposes supplying lubrication oil from below a brake device to cool the brake device by the lubrication oil in order to protect the brake device from frictional heat.
However, when lubrication oil is supplied from below a brake device as proposed in Japanese Patent No. 5,498,785, it takes time until lubrication oil reaches the upper portion of friction plates. As a result, the lower portion of the friction plates may be intensively cooled, and the upper portion of the friction plates may not be sufficiently cooled.